On Feb 1, 2013, at 1:43 PM, Jason Baugher <jason@thebaughers.com> wrote:
It's still a 23dB loss for each customer from the CO to the ONT.
I have an OLT that launches at +5dBm. At 1490nm, I should see about a .26dB loss per km. My 1x32 splitter is going to add about 16dB more loss. Assuming we ignore connector losses, and also assume that the customer is 10km away:
Nope… The power going into each fiber out of the splitter is 1/16th that of what went into the splitter. Yes, your total in-line loss is still 10km, but you are forgetting about the fact that you lost 15/16th of the power effectively going to the fiber when you went through the splitter (in addition to the splitter loss itself). So: CO Based splitter: Each customer gets (IN - 16dB - (10km x .26db))/32 Splitter at 9km: Each customer gets (IN - (9km x .26dB) -16db)/32-(1km x .26db) If we use 5dBm as our input, this works out: CO: (5db - 16db - (10km x .26db) / 32 /32 is effectively -15 db (-3db = ½ power, 32 = 2^5) Substituting: (5db - 16db - 2.6db) -15db = -28.6db to each customer. Spitter at 9km: (5db - (9km x .26db) -16db)/32-(1km x .26db) Substituting: (5db - 2.34db -16db)-15db-.26db = -28.08db to each customer So there is a difference, but it seems rather negligible now that I've run the numbers. However, it's entirely possible that I got this wrong somewhere, so I invite those more expert than I to review the calculations and tell me what I got wrong. Owen
CO-based splitter: +5dBm - 16dB - (10km x .26dB) = -13.6
Splitter at 9km: +5dBm - (9km x .26dB) - 16dB - (1km x .26dB) = -13.6
If someone can explain why this math would be wrong, I'd love to hear it and I'd be happy to run it past our vendor to see if they agree.
On Fri, Feb 1, 2013 at 3:16 PM, Owen DeLong <owen@delong.com> wrote: Actually, this is an issue… I should have seen it.
You have 3 loss components… Power out = (Power in - loss to splitter - splitter loss) / nOut - loss-to-customer
So, if the loss to the splitter is 3db and you have 20db (effective 320db on a 16x split) loss on each customer link, that's a radically worse proposition than 20db loss to the splitter and 3db loss to each customer (which is effectively 48db loss on a 16x split).
It's still do-able, but you either need amplifier(s) or very short distances between the customer and the MMR.
Given this consideration, I think the situation can still be addressed.
Put the splitters in the B-Box and allow for the possibility that each subscriber can be XC to either a splitter or an upstream dedicated fiber. The provider side of each splitter would be connected to an upstream fiber to the MMR.
So, each B-Box contains however many splitters are required and each splitter is connected upstream to a single provider, but you can still have multiple competitive providers in the MMR.
This setup could support both PON and Ethernet as well as other future technologies.
Owen
On Feb 1, 2013, at 1:04 PM, Jason Baugher <jason@thebaughers.com> wrote:
I should clarify: Distance x loss/km + splitter loss. = link loss.
On Fri, Feb 1, 2013 at 3:03 PM, Jason Baugher <jason@thebaughers.com> wrote: I disagree. Loss is loss, regardless of where the splitter is placed in the equation. Distance x loss + splitter insertion loss = total loss for purposes of link budget calculation.
The reason to push splitters towards the customer end is financial, not technical.
On Fri, Feb 1, 2013 at 2:29 PM, Scott Helms <khelms@zcorum.com> wrote: Owen,
You're basing your math off of some incorrect assumptions about PON. I'm actually sympathetic to your goal, but it simply can't work the way you're describing it in a PON network. Also, please don't base logic for open access on meet me rooms, this works in colo spaces and carrier hotels but doesn't in broadband deployments because of economics. If you want to champion this worthy goal you've got to accept that economics is a huge reason why this hasn't happened in the US and is disappearing where it has happened globally.
Bottom line, you've got OLT -> FIBER(of length n) -> splitter -> fiber-drops to each house -> ONT.
So far you're correct.
All I'm proposing is making n really short and making "fiber-drops to each house" really long. I'm not proposing changing the fundamental architecture. Yes, I recognize this changes the economics and may well make PON less attractive than other alternatives. I don't care. That's not a primary concern. The question is "can PON be made to work in this environment?" It appears to me that it can.
Here is where you're problems start. The issue is that the signal *prior to being split* can go 20km if you're splitting it 32 ways (or less) or 10km if you're doing a 64 way split. AFTER the splitter you have a MAX radius of about 1 mile from the splitter.
Here is a good document that describes the problem in some detail:
http://www.ofsoptics.com/press_room/media-pdfs/FTTH-Prism-0909.pdf
Also, here is a proposed spec that would allow for longer runs post splitter with some background on why it can't work in today's GPON deployments.
http://www.ericsson.com/il/res/thecompany/docs/publications/ericsson_review/...
-- Scott Helms Vice President of Technology ZCorum (678) 507-5000 -------------------------------- http://twitter.com/kscotthelms --------------------------------